Disc drive machines record and reproduce information stored on a recording media. Typical hard disc drives, often referred to as Winchester disc drives include a plurality of vertically-aligned, rotating information storage discs, each having at least one associated magnetic read/write head or slider that is adapted to transfer information between the disc and an external computer system. The information storage discs are journaled about a spindle motor assembly capable of rotating the discs at high speeds. Each slider is carried by an elongated flexure arm. The flexure arms, in turn, are vertically aligned and carried by a single head positioner assembly. The head positioner assembly is adapted to move the sliders back and forth in unison across the face of the vertically aligned discs. The head positioner assembly is traditionally either rotationally mounted or takes the form of a carriage that is free to move back and forth along a single axis. In either case, the head positioner assembly is adapted to precisely position the heads relative to the magnetic information storage discs.
A wide variety of flexure arm mounting techniques are known to the prior art. During operation, the sliders and the flexures are occasionally known to fail and require repair. Therefore, it is desireable to provide a flexure mounting structure that allows ready replacement of the flexures. One conventional manner for mounting the head arms utilizes a head positioner assembly having a plurality of vertically aligned support platforms (often referred to as ears). The vertically aligned platforms, together with the base from which they extend are frequently referred to as an E-block. One or two head arms are then mounted to each platform with one or two screws extending vertically through the vertically aligned ears to hold all of the head arms to their respective ears. One drawback of such an approach is that it is extremely important that once set, the heads move laterally as little as possible relative to the head positioner assembly. Movements on the order of several millionths of an inch can cause difficulties. However, in the mounting arrangement described above, internal torsional stresses are induced while initially tightening the screws during assembly. Thermal expansions and contractions within the screws and head positioner assembly can induce additional stresses within the screws. These stresses combine to cause the screws to unwind a minute amount over the operational life of the drive which results in lateral head movements large enough to cause troubles. Therefore, during production, the disc drive must be run through at least one thermal baking and cooling cycle to eliminate thermal stresses within the disc drive components including the flexure mounting arrangement. The thermal baking and cooling cycle is extremely time consuming and creates one of the major production line delays. Therefore, it is desireable to provide a flexure mounting structure that does not require thermal baking and cooling to minimize lateral movements of the heads.
Another approach to mounting head arms to an E-block style head positioning assembly is disclosed in U.S. Pat. No. 4,829,395 to Coon et al.. The load beam/flexure assembly for mini Winchester disc drives described by Coon uses ball staking to form a swage connection between the head arm and the support platform. However, since no more than two head arms are secured by the swaging arrangement disclosed by Coon, an undesirably large number of parts are used to secure a multiplicity of head arms to the E-block. Furthermore, such an arrangement is difficult to disassembly when it becomes necessary to replace a worn slider or flexure assembly.
In recent years there have been several attempts to take advantage of the shape memory metal phenomenon to accomplish electromechanical functions in disc drives. The phenomenon of shape memory is, of course, well understood. It is based on the thermoelastic martensitic transformation which is briefly explained hereunder. A shape memory alloy, such as a Ni-Ti alloy, has a high temperature austenitic phase wherein the crystal structure is body center cubic. When cooled below its transformation temperature, the austenitic structure undergoes a diffusionless shear transform into a highly twined martensitic crystal structure. In the martensitic phase, the alloy is easily deformed by the application of a small external force. However, in the austenitic phase, the alloy is very strong and is not easily deformed. When the alloy is heated through its transformation temperature, the martensitic phase is elastically returned to the austenitic phase (referred to as an inverse transformation) according to a given ordered crystal and orientation law. A notable characteristic of the alloy is the extremely large recovery force that is generated when returning to the austenitic phase. This recovery force can be used advantageously in a wide variety of manners. When properly formed, the shape memory metal also has some shape memory when returning to the martensitic phase.